The concept of incorporating means in a wallet-like structure for monitoring the absence of a credit card from a compartment is well known.
For example, U.S. Pat. No. 3,959,789 discloses a card monitoring means that may be incorporated into a wallet for alerting the user after a card has been removed from its compartment and not returned after a predetermined length of time. The disclosed monitoring means includes a pair of separators mounted in each compartment. The separators carry opposed electrical conductors adapted to be held apart by a credit card accommodated in the compartment and adapted to contact one another when the credit card is removed from the compartment. The conductors are connected in a circuit including timing means which activates an alarm a predetermined time interval after a card is removed from its compartment.
U.S. Pat. No. 4,480,250 also discloses a credit card wallet incorporating a monitoring and alarm system. The wallet includes first and second flaps foldable upon each other. Each of the flaps carries clip switches adapted for receiving credit cards therein. The clip switches are electrically connected in parallel with each other and in series between an alarm and a battery. When a credit card is missing from one of the clip switches, the circuit between the battery and the alarm is completed and the alarm is energized. The flap also includes a proximity switch for disabling the alarm when the flaps are unfolded.
U.S. Pat. No. 4,692,745 also discloses a wallet incorporating a monitoring and alarm system for detecting the absence of a card from a compartment. The system includes a photoconductive means positioned on the inner portion of one of the wallet flaps for disabling the alarm when the wallet is open, i.e. flaps unfolded. When the wallet is closed to thus deprive the photoconductive means of light energy, the alarm will be activated if a card is missing from one of the wallet's compartments.
Although the systems disclosed in the aforementioned patents can all operate satisfactorily under appropriate conditions, they are subject to reliability problems when incorporated in wallets formed of flexible sheet material. More particularly, wallets formed of flexible sheet material are frequently carried in user's hip or side pockets where they are subjected to various forces which, over time, can distort the shape of the wallet and any malleable switch contacts therein, frequently resulting in a malfunctioning of the monitoring and alarm system.